I. Field of the Invention
This invention relates to a method and apparatus utilizing a directed energy beam to selectively deposit material from a gas phase or selectively evaporate material condensed from a gas phase to produce a part. In particular, this invention relates to a method of producing a part utilizing a computer-assisted laser or other directed energy beam apparatus which sequentially deposits or evaporates material that was pre-deposited from a gas phase to build a desired part in a layer by layer fashion.
II. Description of the Relevant Art
The economies associated with conventional part production methods are generally related directly to the quantity of parts to be produced and the desired material characteristics of the finished parts. For example, large scale manufacture casting and extrusion techniques are often cost effective, but these production methods due to costs are generally unacceptable for small quantities--i.e replacement parts or prototype production. Many such conventional part production methods require expensive part specific tooling. Standard powder processing requires die for shaping the powder, making powder processing unattractive as a method for producing a small number of parts.
Where only a small number of parts are desired, conventional production methods involving a subtractive machining method are usually used to produce the desired part. In such subtractive methods, material is cut away from the starting block of material to produce a more complex shape. Examples of subtractive machine tool methods include: milling, drilling, grinding, lathe cutting, flame cutting, electric discharge machine, etc. While such conventional machine tool subtractive methods are usually effective in producing the desired part, they are deficient in many respects.
First, such conventional machine tool subtractive methods produce a large amount of waste material for disposal. Further, such machine tool methods usually involve a large initial expense for setting up the proper machining protocol and tools. As such, the set-up time is not only expensive, but relies a great deal on human judgment and expertise. These problems are, of course, exacerbated when only a small number of parts are to be produced.
Another difficulty associated with such conventional machining techniques involves tool wear--which not only involves the cost of replacement, but also reduces machining accuracy as the tool wears. Another limit on the accuracy and tolerance of any part produced by conventional machining techniques is the tolerance limits inherent in the particular machine tool. For example, in a conventional milling machine or lathe, the lead screws and ways are manufactured to a certain tolerance, which limits the tolerances obtainable in manufacturing a part on a the machine tool. Of course, the tolerances attainable are reduced with age of the machine tool.
The final difficulty associated with such conventional machine tool subtractive processes is the difficulty or impossibility of making many part configurations. That is, conventional machining methods are usually best suited for producing symmetrical parts and parts where only the exterior part is machined. However, where a desired part is unusual in shape or has internal features, the machining becomes more difficult and quite often, the part must be divided into segments for production. In many cases, a particular part configuration is not possible because of the limitations imposed upon the tool placement on the part. Thus, the size and configuration of the cutting tool do not permit access of the tool to produce the desired configuration.
There are other machining processes which are additive, for example, plating, cladding, and some welding processes are additive in that material is added to a starting substrate. In recent years, other additive-type machining methods have been developed which use a laser beam to coat or deposit material on a starting article. Examples include U.S. Pat. Nos. 4,117,302; 4,474,861; 4,300,474; and 4,323,756. These recent uses of lasers have been primarily limited to adding a coating to a previously machined article. Often such laser coating methods have been employed to achieve certain metallurgical properties obtained only by such coating methods. Typically, in such laser coating methods the starting article is rotated and the laser directed at a fixed location with the coating material sprayed onto the article so that the laser will melt the coating onto the article
Additionally, a process for utilizing laser to sinter a powder has been suggested in U.S. Pat. No. 4,863,538 and a process for compressing a powder-based material into a coherent mass prior to sintering has been suggested in U.S. Pat. No. 4,752,352.
A difficulty associated with previously suggested selective sintering methods relates to the problem of evenly depositing the layers of powder for sintering.